Epioblasma torulosa rangiana (Lea) Northern Riffleshell State Distribution Photo by Kevin Cummins, courtesy of the Illinois Natural History Survey Best Survey Period Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Status: Federal and state endangered able sexual dimorphism in riffleshells. Male shells have a sulcus, or ridge, running posterio-ventrally from just Global and State Rank: G2T2/S1 below the beak. Female shells have a low bulge along the posterio-ventral edge of the shell that accommodates Family: Unionidae (Pearly Mussels) the enlarged marsupium containing eggs. Total Range: The northern riffleshell was found Best Survey Time: April through June. historically in Illinois, Indiana, Kentucky, Michigan, Ohio, Pennsylvania, West Virginia, and western Habitat: The northern riffleshell requires swiftly Ontario. It was widespread in the Ohio and Maumee moving, well-oxygenated water. Riffle and run areas River basins, and in tributaries of western Lake Erie. with fine to coarse gravel are the preferred habitats. Today, the northern riffleshell occurs in short reaches of the Green River in Kentucky; the Detroit and Black Biology: The northern riffleshell has been observed to Rivers in Michigan; Big Darby Creek in Ohio; and be gravid from late summer to the following spring, at French Creek, LeBoeuf Creek and the Allegheny River which time the glochidia are released (Ortmann 1912, in Pennsylvania (Stansberry et al. 1982). Clarke 1987). The females use the posterior portion of the outer gill as a brood pouch, or marsupium, that is State Distribution: The range of the northern riffleshell accomodated by the swelling of the female shell. in Michigan is restricted to the eastern border of the Under laboratory conditions, glochidia developed with state. Historically, northern riffleshell mussels occurred brown trout, bluebreast darter, banded darter and in the Black River in Sanilac Co.; Lake St. Clair and the banded sculpin hosts (O’Dee and Watters 1998). Detroit and Huron Rivers in Wayne Co.; and Macon However, these fish species do not occur in the Creek and the River Raisin in Monroe Co. Over the Michigan range of the riffleshell, suggesting that there past 20 years, northern riffleshells have only been found are additional hosts yet to be identified (Goforth 1999). in the Black, St. Clair and Detroit Rivers. Glochidia are semicircular in shape, with a straight hinge line and no hooks. It is unknown at what age Recognition: The northern riffleshell is of moderate riffleshells are reproductively mature. Because of their size with large adults reaching two inches. The shell is small size, it is difficult to determine whether juveniles ovate to quadrate in shape, becoming thicker anteriorly. are present in a population. This species may reach 15 The shell is light green-yellow to olive green, with dark, years of age based on studies of annular growth rings. narrow, closely-spaced rays. The hinge teeth are Like all mussels, the northern riffleshell is a filter medium-sized and well developed. There is consider- feeder. Because the riffleshell filters the water for food Michigan Natural Features Inventory P.O. Box 30444 - Lansing, MI 48909-7944 Phone: 517-373-1552 northern riffleshell, page 2 and oxygen, high levels of siltation can smother siphon- O’Dee, S.H. and G.T. Watters. 1998. New or confirmed ing mussels. The exotic zebra mussel is a threat to the host identifications for eleven freshwater mollusks. riffleshell, not only due to competition for food, but also Unpublished report, School of Natural Resources, because zebra mussels attach to the shells of native The Ohio State University. mussels making it difficult for the mussels to move and feed properly. Stansbery, D.H., K.G. Borror and K.E. Newman. 1982. Biological abstracts of selected species of Unionid The riffleshell occurs at two sites in Michigan, the mollusks recovered from Ohio. Unpublished. Black River in Sanilac Co. and the Detroit River in Prepared for the Ohio Heritage Foundation, Ohio Wayne Co. Historically, the Black River has had a Department of Natural Resources. strong population of riffleshells. However, dredging of the river in 1948 and 1989 decimated this population. Trdan, R.J., W.R. Hoeh and S.E. Cordoba. 1987. Viable No live individuals were found at these sites in 1998, populations of Dysnomia torulosa, an endangered although recently spent shells found indicate that there freshwater mussel, in the Black River of Sanilac may still be some individuals remaining. The Detroit County, Michigan. Unpublished. Prepared for the River may still have a viable reproducing population, Michigan Department of Natural Resources, despite human impacts and zebra mussel infestations in Nongame Wildlife Unit. the river. In 1992, a “Rescue the Riffleshell” program transplanted 110 mussels from the Detroit River to the United State Fish and Wildlife Service. 1994. Clubshell St. Clair River. The current status of this translocation (Pleurobema clava) and northern riffleshell is unknown. (Epioblasma torulosa rangiana) recovery plan. Hadley, Massachusetts. 68 pp. Conservation/Management: The future of the north- ern riffleshell depends on the protection and preserva- tion of habitat and host fish. Siltation and run-off must Abstract citation: be reduced to facilitate the recovery of this species. Damming and dredging of rivers have had a negative Carman, S. and R. R. Goforth. 2000. Special animal effect on the riffleshell, altering fast flowing, clear water abstract for Epioblasma torulosa rangiana (north- habitats and making them unsuitable for sustaining ern riffleshell mussel). Michigan Natural Features riffleshell populations. The continued spread of exotic Inventory, Lansing, MI. 2pp. species such as the zebra mussel throughout Great Lakes tributary rivers is a continuing and increasing threat to all native species. Transplantation of viable populations into more protected and preserved habitats may be required to insure the long-term viability of this species. Research Needs: To protect and preserve the reduced populations of northern riffleshells in Michigan, life history and ecological requirements for this species must be better understood. Perhaps of greatest impor- tance is the identification of successful host species so that these fish can be protected as well. Selected References: Clarke, C.F. 1987. The freshwater naiads of Ohio, Part II. Maumee River drainage. Unpublished report. 116 pp. Goforth, R.R. 1999. Surveys for the Northern Riffleshell Copyright 2004 Michigan State University Board of Trustees. (Epioblasma torulosa rangiana) and other rare clams in Michigan. Unpublished Report. 25 pp. Michigan State University Extension is an affirmative-action, equal-opportunity organization. Hoeh, W.R. and R.J. Trdan. 1985. Freshwater mussels Funding for abstract provided by Michigan Department of (Pelecypoda:Unionidae) of the major tributaries of Natural Resources-Forest Management Division and the St. Clair River, Michigan. Malacological Wildlife Division. Review 18:115-116. Michigan Natural Features Inventory P.O. Box 30444 - Lansing, MI 48909-7944 Phone: 517-373-1552.